Processes for producing anhydrous ethanol compositions

ABSTRACT

In one embodiment, the present invention is to a process for producing a anhydrous ethanol composition comprising hydrogenating acetic acid in the presence of a catalyst to form a crude ethanol product; separating in a first column at least a portion of the crude ethanol product into a first distillate comprising ethanol, water and ethyl acetate, and a first residue comprising acetic acid; separating in a second column at least a portion of the first distillate into a second distillate comprising ethyl acetate and a second residue comprising ethanol and water; separating in a third column at least a portion of the second residue into a third distillate comprising ethanol and residual water and a third residue comprising separated water; and dehydrating at least a portion of the third distillate to form the anhydrous ethanol composition. The anhydrous ethanol composition, as formed, comprises less than 1 wt. % water, based on the total weight of the anhydrous ethanol composition.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application No.61/332,726, filed on May 7, 2010 and to U.S. Provisional Application No.61/300,815, filed on Feb. 2, 2010, the entire contents and disclosuresof which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to processes for producing ananhydrous ethanol composition. In particular, the present inventionrelates to processes for producing an anhydrous ethanol composition viathe hydrogenation of acetic acid.

BACKGROUND OF THE INVENTION

Ethanol is a particularly valuable alcohol that has a broad range ofapplications such as chemical solvents; feedstocks for various chemicalsyntheses; consumable products, e.g., beer, wine, and spirits; andfuels.

The hydrogenation of alkanoic acids and/or other carbonylgroup-containing compounds is one method of producing alcohols such asethanol. This method has been widely studied. As a result, a variety ofrelated combinations of reactants, catalysts, supports, and operatingconditions have been mentioned in literature.

Anhydrous ethanol, however, is preferred for some ethanol applications,e.g., fuels. Anhydrous or substantially anhydrous ethanol, however, isoften difficult to obtain from conventional hydrogenation and separationprocesses. For example, the ethanol and water produced in conventionalhydrogenation reactions may form a binary azeotrope. This azeotropecontains about 95% ethanol and about 5% water. Because the boiling pointof this azeotrope (78° C.) is just slightly below that of pure ethanol(78.4° C.), an anhydrous or substantially anhydrous ethanol compositionis difficult to obtain from a crude ethanol composition via simple,conventional distillation.

Even though some hydrogenation and separation techniques may be known,the need exists for an improved process and system for producinganhydrous ethanol compositions.

SUMMARY OF THE INVENTION

The present invention is directed to a process for producing anhydrousethanol compositions. The process comprises the step of hydrogenatingacetic acid in the presence of a catalyst to form a crude ethanolproduct. In one embodiment, the process further comprises the step ofseparating in a first column at least a portion of the crude ethanolproduct into a first distillate and a first residue. The firstdistillate comprises ethanol, water, and ethyl acetate. The firstresidue comprises acetic acid. The process further comprises the step ofseparating in a second column at least a portion of the first distillateinto a second distillate and a second residue. The first distillatecomprises ethyl acetate and the second residue comprises ethanol andwater. The process further comprises the step of separating in a thirdcolumn at least a portion of the second residue into a third distillateand a third residue. The third distillate comprises ethanol and residualwater and the third residue comprises separated water. The processfurther comprises the step of dehydrating at least a portion of thethird distillate to form the anhydrous ethanol composition. Theanhydrous ethanol composition, as formed, comprises less than 1 wt. %water, e.g., less than 0.5 wt. %, less than 0.1 wt. %, less than 0.01wt. %, less than 0.001 wt. %, or less than 0.0001 wt. %. In terms ofranges, the anhydrous ethanol composition comprises from 0.0001 wt. % to1 wt. % water, e.g., from 0.001 wt. % to 0.5 wt. %, or from 0.001 wt. %to 0.05 wt. %. The weight percentages are based on the total weight ofthe anhydrous ethanol composition. Preferably, the anhydrous ethanolcomposition formed by the inventive process comprises from 95 wt. % to99.9999 wt. % ethanol and from 0.0001 wt. % to 1 wt. % water. In oneexample, the third distillate comprises from 0.0001 wt. % to 12 wt. %water and/or the dehydrating step removes at least 50 wt. % of the waterfrom the third distillate.

Preferably, the dehydrating step comprises separating in a fourth columnat least a portion of the third distillate into a fourth distillate anda fourth residue. The fourth distillate comprises the anhydrous ethanolcomposition and the fourth residue comprises water. In one embodiment,the fourth column is an extractive distillation column comprising from10 to 100 trays. Preferably, the extractive distillation columncomprises at least one extraction agent selected from the groupconsisting of glycols, glycerol, gasoline, and hexane. In anotherembodiment, a molecular sieve unit dehydrates the third distillate. Inanother embodiment, a membrane separation unit dehydrates the thirddistillate.

In another embodiment, the invention relates to a system for producinganhydrous ethanol compositions. The system comprises a reactor forhydrogenating acetic acid in the presence of a catalyst to form a crudeethanol product. The system further comprises a first column forseparating at least a portion of the crude ethanol product into a firstdistillate and a first residue. The system further comprises a secondcolumn for separating at least a portion of the first distillate into asecond distillate and a second residue. The system further comprises athird column for separating at least a portion of the second residueinto a third distillate and a third residue. The system furthercomprises a dehydrator for dehydrating at least a portion of the thirddistillate to form the anhydrous ethanol composition. Exemplarydehydrators include an extractive distillation column, a molecular sieveunit, a membrane separation unit, and combinations thereof.

BRIEF DESCRIPTION OF DRAWINGS

The invention is described in detail below with reference to theappended drawings, wherein like numerals designate similar parts.

FIG. 1A is a schematic diagram of a hydrogenation system having a fourthcolumn in accordance with one embodiment of the present invention.

FIG. 1B is a schematic diagram of a hydrogenation system having amolecular sieve unit in accordance with one embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION Introduction

The present invention relates to processes for producing anhydrousethanol compositions. In one embodiment, the anhydrous ethanolcomposition is separated from a crude acetic acid product that isproduced via hydrogenation of acetic acid. The hydrogenation may beperformed in the presence of a catalyst. The separating may be performedin one or more separation units, e.g., distillation columns, e.g., twoor more, or three or more. In a preferred embodiment, the processincludes the step of dehydrating an ethanol enriched stream derived fromthe crude ethanol product to yield the anhydrous ethanol composition.The anhydrous ethanol composition comprises ethanol and less than 1 wt.% water, e.g., less than 0.5 wt. %, less than 0.1 wt. %, less than 0.01wt. %, less than 0.001 wt. %, or less than 0.0001 wt. %, based on thetotal weight of the anhydrous ethanol composition. In terms of ranges,depending largely on the dehydration technique employed, the anhydrousethanol composition may comprise from 0.0001 wt. % to 1 wt. % water,e.g., from 0.001 to 0.5 wt. % or from 0.001 to 0.05 wt. %, based on thetotal weight of the anhydrous ethanol composition.

Hydrogenation Process

The hydrogenation of acetic acid to form ethanol and water may berepresented by the following reaction:

Suitable hydrogenation catalysts include catalysts comprising a firstmetal and optionally one or more of a second metal, a third metal oradditional metals, optionally on a catalyst support. The first andoptional second and third metals may be selected from Group IB, IIB,IIIB, IVB, VB, VIIB, VIIB, VIII transitional metals, a lanthanide metal,an actinide metal or a metal selected from any of Groups IIIA, IVA, VA,and VIA. Preferred metal combinations for some exemplary catalystcompositions include platinum/tin, platinum/ruthenium, platinum/rhenium,palladium/ruthenium, palladium/rhenium, cobalt/palladium,cobalt/platinum, cobalt/chromium, cobalt/ruthenium, silver/palladium,copper/palladium, nickel/palladium, gold/palladium, ruthenium/rhenium,and ruthenium/iron. Exemplary catalysts are further described in U.S.Pat. No. 7,608,744 and U.S. Publication Nos. 2010/0029995 and2010/0197485, the entireties of which are incorporated herein byreference.

In one exemplary embodiment, the catalyst comprises a first metalselected from the group consisting of copper, iron, cobalt, nickel,ruthenium, rhodium, palladium, osmium, iridium, platinum, titanium,zinc, chromium, rhenium, molybdenum, and tungsten. Preferably, the firstmetal is selected from the group consisting of platinum, palladium,cobalt, nickel, and ruthenium. More preferably, the first metal isselected from platinum and palladium. When the first metal comprisesplatinum, it is preferred that the catalyst comprises platinum in anamount less than 5 wt. %, e.g., less than 3 wt. % or less than 1 wt. %,due to the high demand for platinum.

As indicated above, the catalyst optionally further comprises a secondmetal, which typically would function as a promoter. If present, thesecond metal preferably is selected from the group consisting of copper,molybdenum, tin, chromium, iron, cobalt, vanadium, tungsten, palladium,platinum, lanthanum, cerium, manganese, ruthenium, rhenium, gold, andnickel. More preferably, the second metal is selected from the groupconsisting of copper, tin, cobalt, rhenium, and nickel. More preferably,the second metal is selected from tin and rhenium.

If the catalyst includes two or more metals, e.g., a first metal and asecond metal, the first metal optionally is present in the catalyst inan amount from 0.1 wt. % to 10 wt. %, e.g., from 0.1 wt. % to 5 wt. %,or from 0.1 wt. % to 3 wt. %. The second metal preferably is present inan amount from 0.1 wt. % and 20 wt. %, e.g., from 0.1 wt. % to 10 wt. %,or from 0.1 wt. % to 5 wt. %. For catalysts comprising two or moremetals, the two or more metals may be alloyed with one another or maycomprise a non-alloyed metal solution or mixture.

The preferred metal ratios may vary depending on the metals used in thecatalyst. In some exemplary embodiments, the mole ratio of the firstmetal to the second metal is from 10:1 to 1:10, e.g., from 4:1 to 1:4,from 2:1 to 1:2, from 1.5:1 to 1:1.5 or from 1.1:1 to 1:1.1.

The catalyst may also comprise a third metal selected from any of themetals listed above in connection with the first or second metal, solong as the third metal is different from the first and second metals.In preferred aspects, the third metal is selected from the groupconsisting of cobalt, palladium, ruthenium, copper, zinc, platinum, tin,and rhenium. More preferably, the third metal is selected from cobalt,palladium, and ruthenium. When present, the total weight of the thirdmetal preferably is from 0.05 wt. % and 4 wt. %, e.g., from 0.1 wt. % to3 wt. %, or from 0.1 wt. % to 2 wt. %.

In addition to one or more metals, the exemplary catalysts furthercomprise a support or a modified support, meaning a support thatincludes a support material and a support modifier, which adjusts theacidity of the support material. The total weight of the support ormodified support, based on the total weight of the catalyst, preferablyis from 75 wt. % to 99.9 wt. %, e.g., from 78 wt. % to 97 wt. %, or from80 wt. % to 95 wt. %. In preferred embodiments that use a modifiedsupport, the support modifier is present in an amount from 0.1 wt. % to50 wt. %, e.g., from 0.2 wt. % to 25 wt. %, from 0.5 wt. % to 15 wt. %,or from 1 wt. % to 8 wt. %, based on the total weight of the catalyst.

Suitable support materials may include, for example, stable metaloxide-based supports or ceramic-based supports. Preferred supportsinclude silicaceous supports, such as silica, silica/alumina, a GroupIIA silicate such as calcium metasilicate, pyrogenic silica, high puritysilica, and mixtures thereof. Other supports may include, but are notlimited to, iron oxide, alumina, titania, zirconia, magnesium oxide,carbon, graphite, high surface area graphitized carbon, activatedcarbons, and mixtures thereof.

In the production of ethanol, the catalyst support may be modified witha support modifier. Preferably, the support modifier is a basic modifierthat has a low volatility or no volatility. Such basic modifiers, forexample, may be selected from the group consisting of: (i) alkalineearth oxides, (ii) alkali metal oxides, (iii) alkaline earth metalmetasilicates, (iv) alkali metal metasilicates, (v) Group IIB metaloxides, (vi) Group IIB metal metasilicates, (vii) Group IIIB metaloxides, (viii) Group IIIB metal metasilicates, and mixtures thereof. Inaddition to oxides and metasilicates, other types of modifiers includingnitrates, nitrites, acetates, and lactates may be used. Preferably, thesupport modifier is selected from the group consisting of oxides andmetasilicates of any of sodium, potassium, magnesium, calcium, scandium,yttrium, and zinc, as well as mixtures of any of the foregoing.Preferably, the support modifier is a calcium silicate, and morepreferably calcium metasilicate (CaSiO₃). If the support modifiercomprises calcium metasilicate, it is preferred that at least a portionof the calcium metasilicate is in crystalline form.

A preferred silica support material is SS61138 High Surface Area (HSA)Silica Catalyst Carrier from Saint Gobain N or Pro. The Saint-Gobain Nor Pro SS61138 silica contains approximately 95 wt. % high surface areasilica; a surface area of about 250 m²/g; a median pore diameter ofabout 12 nm; an average pore volume of about 1.0 cm³/g as measured bymercury intrusion porosimetry and a packing density of about 0.352 g/cm³(22 lb/ft³).

A preferred silica/alumina support material is KA-160 (Sud Chemie)silica spheres having a nominal diameter of about 5 mm, a density ofabout 0.562 g/ml, in absorptivity of about 0.583 g H₂O/g support, asurface area of about 160 to 175 m²/g, and a pore volume of about 0.68ml/g.

As will be appreciated by those of ordinary skill in the art, supportmaterials are selected such that the catalyst system is suitably active,selective and robust under the process conditions employed for theformation of ethanol.

The metals of the catalysts may be dispersed throughout the support,coated on the outer surface of the support (egg shell) or decorated onthe surface of the support.

The catalyst compositions suitable for use with the present inventionpreferably are formed through metal impregnation of the modifiedsupport, although other processes such as chemical vapor deposition mayalso be employed. Such impregnation techniques are described in U.S.Pat. No. 7,608,744, U.S. Publication No. 2010/0029995, and U.S.application Ser. No. 12/698,968, referred to above, the entireties ofwhich are incorporated herein by reference.

Some embodiments of the process of hydrogenating acetic acid to formethanol according to one embodiment of the invention may include avariety of configurations using a fixed bed reactor or a fluidized bedreactor, as one of skill in the art will readily appreciate. In manyembodiments of the present invention, an “adiabatic” reactor can beused; that is, there is little or no need for internal plumbing throughthe reaction zone to add or remove heat. In other embodiments, radialflow reactor or reactors may be employed, or a series of reactors may beemployed with or with out heat exchange, quenching, or introduction ofadditional feed material. Alternatively, a shell and tube reactorprovided with a heat transfer medium may be used. In many cases, thereaction zone may be housed in a single vessel or in a series of vesselswith heat exchangers therebetween.

In preferred embodiments, the catalyst is employed in a fixed bedreactor, e.g., in the shape of a pipe or tube, where the reactants,typically in the vapor form, are passed over or through the catalyst.Other reactors, such as fluid or ebullient bed reactors, can beemployed. In some instances, the hydrogenation catalysts may be used inconjunction with an inert material to regulate the pressure drop of thereactant stream through the catalyst bed and the contact time of thereactant compounds with the catalyst particles.

The hydrogenation reaction may be carried out in either the liquid phaseor vapor phase. Preferably, the reaction is carried out in the vaporphase under the following conditions. The reaction temperature may rangefrom 125° C. to 350° C., e.g., from 200° C. to 325° C., from 225° C. to300° C., or from 250° C. to 300° C. The pressure may range from 10 KPato 3000 KPa (about 1.5 to 435 psi), e.g., from 50 KPa to 2300 KPa, orfrom 100 KPa to 1500 KPa. The reactants may be fed to the reactor at agas hourly space velocity (GHSV) of greater than 500 hr⁻¹, e.g., greaterthan 1000 hr⁻¹, greater than 2500 hr⁻¹ or even greater than 5000 hr⁻¹.In terms of ranges the GHSV may range from 50 hr⁻¹ to 50,000 hr⁻¹, e.g.,from 500 hr⁻¹ to 30,000 hr⁻¹, from 1000 hr⁻¹ to 10,000 hr⁻¹, or from1000 hr⁻¹ to 6500 hr⁻¹.

The hydrogenation optionally is carried out at a pressure justsufficient to overcome the pressure drop across the catalytic bed at theGHSV selected, although there is no bar to the use of higher pressures,it being understood that considerable pressure drop through the reactorbed may be experienced at high space velocities, e.g., 5000 hr⁻¹ or6,500 hr⁻¹.

Although the reaction consumes two moles of hydrogen per mole of aceticacid to produce one mole of ethanol, the actual molar ratio of hydrogento acetic acid in the feed stream may vary from about 100:1 to 1:100,e.g., from 50:1 to 1:50, from 20:1 to 1:2, or from 12:1 to 1:1. Mostpreferably, the molar ratio of hydrogen to acetic acid is greater than2:1, e.g., greater than 4:1 or greater than 8:1.

Contact or residence time can also vary widely, depending upon suchvariables as amount of acetic acid, catalyst, reactor, temperature andpressure. Typical contact times range from a fraction of a second tomore than several hours when a catalyst system other than a fixed bed isused, with preferred contact times, at least for vapor phase reactions,of from 0.1 to 100 seconds, e.g., from 0.3 to 80 seconds or from 0.4 to30 seconds.

The raw materials, acetic acid and hydrogen, used in connection with theprocess of this invention may be derived from any suitable sourceincluding natural gas, petroleum, coal, biomass, and so forth. Asexamples, acetic acid may be produced via methanol carbonylation,acetaldehyde oxidation, ethylene oxidation, oxidative fermentation, andanaerobic fermentation. As petroleum and natural gas prices fluctuate,becoming either more or less expensive, methods for producing aceticacid and intermediates such as methanol and carbon monoxide fromalternate carbon sources have drawn increasing interest. In particular,when petroleum is relatively expensive compared to natural gas, it maybecome advantageous to produce acetic acid from synthesis gas (“syngas”) that is derived from any available carbon source. U.S. Pat. No.6,232,352, the disclosure of which is incorporated herein by reference,for example, teaches a method of retrofitting a methanol plant for themanufacture of acetic acid. By retrofitting a methanol plant, the largecapital costs associated with carbon monoxide generation for a newacetic acid plant are significantly reduced or largely eliminated. Allor part of the syn gas is diverted from the methanol synthesis loop andsupplied to a separator unit to recover carbon monoxide and hydrogen,which are then used to produce acetic acid. In addition to acetic acid,such a process can also be used to make hydrogen which may be utilizedin connection with this invention.

Methanol carbonylation processes suitable for production of acetic acidare described in U.S. Pat. Nos. 7,208,624, 7,115,772, 7,005,541,6,657,078, 6,627,770, 6,143,930, 5,599,976, 5,144,068, 5,026,908,5,001,259, and 4,994,608, the disclosures of which are incorporatedherein by reference. Optionally, the production of ethanol may beintegrated with such methanol carbonylation processes.

U.S. Pat. No. RE 35,377 also incorporated herein by reference, providesa method for the production of methanol by conversion of carbonaceousmaterials such as oil, coal, natural gas and biomass materials. Theprocess includes hydrogasification of solid and/or liquid carbonaceousmaterials to obtain a process gas which is steam pyrolized withadditional natural gas to form synthesis gas. The syn gas is convertedto methanol which may be carbonylated to acetic acid. The methodlikewise produces hydrogen which may be used in connection with thisinvention as noted above. U.S. Pat. No. 5,821,111, which discloses aprocess for converting waste biomass through gasification into synthesisgas as well as U.S. Pat. No. 6,685,754, the disclosures of which areincorporated herein by reference.

In one optional embodiment, the acetic acid feed stream fed to thehydrogenation reaction comprises acetic acid and may also comprise othercarboxylic acids, e.g., propionic acid, esters, and anhydrides, as wellas acetaldehyde and acetone. In one embodiment, the acetic acid fed tothe hydrogenation reaction comprises propionic acid. For example thepropionic acid in the acetic acid feed stream may range from 0.001 wt. %to 15 wt. %, e.g., from 0.001 wt. % to 0.1 wt. %, from 0.125 wt. % to12.5 wt. %, from 1.25 wt. % to 11.25 wt. %, or from 3.75 wt. % to 8.75wt. %. Thus, the acetic acid feed stream may be a cruder acetic acidfeed stream, e.g., a less-refined acetic acid feed stream.

Alternatively, acetic acid in vapor form may be taken directly as crudeproduct from the flash vessel of a methanol carbonylation unit of theclass described in U.S. Pat. No. 6,657,078, the entirety of which isincorporated herein by reference. The crude vapor product, for example,may be fed directly to the ethanol synthesis reaction zones of thepresent invention without the need for condensing the acetic acid andlight ends or removing water, saving overall processing costs.

The acetic acid may be vaporized at the reaction temperature. Followingthe vaporization, the vaporized acetic acid can be fed along withhydrogen in an undiluted state or diluted with a relatively inertcarrier gas, such as nitrogen, argon, helium, carbon dioxide and thelike. For reactions run in the vapor phase, the temperature should becontrolled in the system such that it does not fall below the dew pointof acetic acid. In one embodiment the acetic acid may be vaporized atthe boiling point of acetic acid at the particular pressure, and thenthe vaporized acetic acid may be further heated to the reactor inlettemperature. In another embodiment, the acetic acid is transferred tothe vapor state by passing hydrogen, recycle gas, another suitable gas,or mixtures thereof through the acetic acid at a temperature below theboiling point of acetic acid, thereby humidifying the carrier gas withacetic acid vapors, followed by heating the mixed vapors up to thereactor inlet temperature. Preferably, the acetic acid is transferred tothe vapor by passing hydrogen and/or recycle gas through the acetic acidat a temperature at or below 125° C., followed by heating of thecombined gaseous stream to the reactor inlet temperature.

In particular, the hydrogenation of acetic acid may achieve favorableconversion of acetic acid and favorable selectivity and productivity toethanol. For purposes of the present invention, the term “conversion”refers to the amount of acetic acid in the feed that is converted to acompound other than acetic acid. Conversion is expressed as a molepercentage based on acetic acid in the feed. The conversion may be atleast 10%, e.g., at least 20%, at least 40%, at least 50%, at least 60%,at least 70% or at least 80%. Although catalysts that have highconversions are desirable, such as at least 80% or at least 90%, in someembodiments a low conversion may be acceptable at high selectivity forethanol. It is, of course, well understood that in many cases, it ispossible to compensate for conversion by appropriate recycle streams oruse of larger reactors, but it is more difficult to compensate for poorselectivity.

Selectivity is expressed as a mole percent based on converted aceticacid. It should be understood that each compound converted from aceticacid has an independent selectivity and that selectivity is independentfrom conversion. For example, if 50 mole % of the converted acetic acidis converted to ethanol, we refer to the ethanol selectivity as 50%.Preferably, the catalyst selectivity to ethoxylates is at least 60%,e.g., at least 70%, or at least 80%. As used herein, the term“ethoxylates” refers specifically to the compounds ethanol,acetaldehyde, and ethyl acetate. Preferably, the selectivity to ethanolis at least 80%, e.g., at least 85% or at least 88%. Preferredembodiments of the hydrogenation process also have low selectivity toundesirable products, such as methane, ethane, and carbon dioxide. Theselectivity to these undesirable products preferably is less than 4%,e.g., less than 2% or less than 1%. More preferably, these undesirableproducts are not detectable. Formation of alkanes may be low, andideally less than 2%, less than 1%, or less than 0.5% of the acetic acidpassed over the catalyst is converted to alkanes, which have littlevalue other than as fuel.

The term “productivity,” as used herein, refers to the grams of aspecified product, e.g., ethanol, formed during the hydrogenation basedon the kilograms of catalyst used per hour. A productivity of at least200 grams of ethanol per kilogram catalyst per hour, e.g., at least 400or at least 600 grams, is preferred. In terms of ranges, theproductivity preferably is from 200 to 3,000 grams of ethanol perkilogram catalyst per hour, e.g., from 400 to 2,500 or from 600 to2,000.

In various embodiments, the crude ethanol product produced by thehydrogenation process, before any subsequent processing, such aspurification and separation, will typically comprise unreacted aceticacid, ethanol, and water. As used herein, the term “crude ethanolproduct” refers to any composition comprising from 5 wt. % to 70 wt. %ethanol and from 5 wt. % to 35 wt. % water. In some exemplaryembodiments, the crude ethanol product comprises ethanol in an amountfrom 5 wt. % to 70 wt. %, e.g., from 10 wt. % to 60 wt. %, or from 15wt. % to 50 wt. %, based on the total weight of the crude ethanolproduct. Preferably, the crude ethanol product contains at least 10 wt.% ethanol, at least 15 wt. % ethanol, or at least 20 wt. % ethanol.

The crude ethanol product typically will further comprise unreactedacetic acid, depending on conversion, for example, in an amount of lessthan 90 wt. %, e.g., less than 80 wt. % or less than 70 wt. %. In termsof ranges, the unreacted acetic acid is preferably present in amountsfrom 0 wt. % to 90 wt. %, e.g., from 5 wt. % to 80 wt. %, from 15 wt. %to 70 wt. %, from 20 wt. % to 70 wt. % or from 25 wt. % to 65 wt. %. Aswater is formed in the reaction process, the crude ethanol product willgenerally comprise water, for example, in amounts ranging from 5 wt. %to 35 wt. %, e.g., from 10 wt. % to 30 wt. % or from 10 wt. % to 26 wt.%. Ethyl acetate may also be produced during the hydrogenation of aceticacid or through side reactions. In these embodiments, the crude ethanolproduct comprises ethyl acetate in amounts ranging from 0 wt. % to 20wt. %, e.g., from 0 wt. % to 15 wt. %, from 1 wt. % to 12 wt. % or from3 wt. % to 10 wt. %. Acetaldehyde may also be produced through sidereactions. In these embodiments, the crude ethanol product comprisesacetaldehyde in amounts ranging from 0 wt. % to 10 wt. %, e.g., from 0wt. % to 3 wt. %, from 0.1 wt. % to 3 wt % or from 0.2 wt. % to 2 wt. %.

Other components, such as, for example, esters, ethers, aldehydes,ketones, alkanes, and carbon dioxide, if detectable, collectively may bepresent in amounts less than 10 wt. %, e.g., less than 6 wt. %, or lessthan 4 wt. %. In terms of ranges, the crude ethanol composition maycomprise the other components in an amount from 0.1 wt. % to 10 wt. %,e.g., from 0.1 wt. % to 6 wt. %, or from 0.1 wt. % to 4 wt. %. Exemplaryembodiments of crude ethanol compositional ranges are provided in Table1.

TABLE 1 CRUDE ETHANOL PRODUCT COMPOSITIONS Conc. Conc. Conc. Conc.Component (wt. %) (wt. %) (wt. %) (wt. %) Ethanol 5 to 70 10 to 60 15 to50 25 to 50 Acetic Acid 0 to 90  5 to 80 15 to 70 20 to 70 Water 5 to 35 5 to 30 10 to 30 10 to 26 Ethyl Acetate 0 to 20  0 to 15  1 to 12  3 to10 Acetaldehyde 0 to 10 0 to 3 0.1 to 3   0.2 to 2   Others 0.1 to 10  0.1 to 6   0.1 to 4   —Purification

FIGS. 1A and 1B show a hydrogenation system 100 suitable for thehydrogenation of acetic acid and the separation of an anhydrous ethanolcomposition from the crude reaction mixture according to one embodimentof the invention. System 100 comprises reaction zone 101 anddistillation zone 102. Reaction zone 101 comprises reactor 103, hydrogenfeed line 104 and acetic acid feed line 105. In FIG. 1A, distillationzone 102 comprises flasher 106, first column 107, second column 108,third column 109, and fourth column 122. In FIG. 1B distillation zone102 comprises flasher 106, first column 107, second column 108, thirdcolumn 109, and molecular sieve unit 124. Hydrogen and acetic acid arefed to a vaporizer 110 via lines 104 and 105, respectively, to create avapor feed stream in line 111 that is directed to reactor 103. In oneembodiment, lines 104 and 105 may be combined and jointly fed to thevaporizer 110, e.g., in one stream containing both hydrogen and aceticacid. The temperature of the vapor feed stream in line 111 is preferablyfrom 100° C. to 350° C., e.g., from 120° C. to 310° C. or from 150° C.to 300° C. Any feed that is not vaporized is removed from vaporizer 110,as shown in FIG. 1A, and may be recycled thereto. In addition, althoughFIG. 1A shows line 111 being directed to the top of reactor 103, line111 may be directed to the side, upper portion, or bottom of reactor103.

Reactor 103 contains the catalyst used in the hydrogenation of thecarboxylic acid, preferably acetic acid. In one embodiment, one or moreguard beds (not shown) may be used to protect the catalyst from poisonsor undesirable impurities contained in the feed or return/recyclestreams. Such guard beds may be employed in the vapor or liquid streams.Suitable guard bed materials are known in the art and include, forexample, carbon, silica, alumina, ceramic, or resins. In one aspect, theguard bed media is functionalized to trap particular species such assulfur or halogens. During the hydrogenation process, a crude ethanolproduct stream is withdrawn, preferably continuously, from reactor 103via line 112. The crude ethanol product stream may be condensed and fedto flasher 106, which, in turn, provides a vapor stream and a liquidstream. The flasher 106, in one embodiment, preferably operates at atemperature of from 50° C. to 500° C., e.g., from 70° C. to 400° C. orfrom 100° C. to 350° C. In one embodiment, flasher 106 operates at apressure ranging from 50 KPa to 2000 KPa, e.g., from 75 KPa to 1500 KPaor from 100 to 1000 KPa. In one preferred embodiment, the temperatureand pressure of flasher 106 is similar to the temperature and pressureof reactor 103.

The vapor stream exiting the flasher 106 may comprise hydrogen andhydrocarbons, which may be purged and/or returned to reaction zone 101via line 113. As shown in FIG. 1A, the returned portion of the vaporstream passes through compressor 114 and is combined with the hydrogenfeed and co-fed to vaporizer 110.

The liquid from flasher 106 is withdrawn and pumped as a feedcomposition via line 115 to the side of first column 107, also referredto as the acid separation column. The contents of line 115 typicallywill be substantially similar to the product obtained directly from thereactor, and may, in fact, also be characterized as a crude ethanolproduct. However, the feed composition in line 115 preferably hassubstantially no hydrogen, carbon dioxide, methane or ethane, which areremoved by flasher 106. Exemplary components of liquid in line 115 areprovided in Table 2. It should be understood that liquid line 115 maycontain other components, not listed, such as components in the feed.

TABLE 2 FEED COMPOSITION Conc. (wt. %) Conc. (wt. %) Conc. (wt. %)Ethanol 5 to 70 10 to 60  15 to 50 Acetic Acid <90 5 to 80 15 to 70Water 5 to 35 5 to 30 10 to 30 Ethyl Acetate <20 0.001 to 15     1 to 12Acetaldehyde <10 0.001 to 3    0.1 to 3   Acetal <5 0.001 to 2 0.005 to1    Acetone <5 0.0005 to 0.05   0.001 to 0.03  Other Esters <5 <0.005<0.001 Other Ethers <5 <0.005 <0.001 Other Alcohols <5 <0.005 <0.001

The amounts indicated as less than (<) in the tables throughout presentapplication are preferably not present and if present may be present intrace amounts or in amounts greater than 0.0001 wt. %.

The “other esters” in Table 2 may include, but are not limited to, ethylpropionate, methyl acetate, isopropyl acetate, n-propyl acetate, n-butylacetate or mixtures thereof. The “other ethers” in Table 2 may include,but are not limited to, diethyl ether, methyl ethyl ether, isobutylethyl ether or mixtures thereof. The “other alcohols” in Table 2 mayinclude, but are not limited to, methanol, isopropanol, n-propanol,n-butanol or mixtures thereof. In one embodiment, the feed composition,e.g., line 115, may advantageously comprise propanol, e.g., isopropanoland/or n-propanol, in small amounts, e.g., from 0.001 wt. % to 0.1 wt.%, from 0.001 wt. % to 0.05 wt. % or from 0.001 wt. % to 0.03 wt. %. Asa result of the low concentration of these other alcohols in the feedcomposition, the resultant anhydrous ethanol composition advantageouslycomprises the alcohols, if at all, only in trace amounts (see discussionbelow). These trace amounts are significantly lower than those levelsobtained via methods that do not utilize the hydrogenantion of aceticacid. It should be understood that these other components may be carriedthrough in any of the distillate or residue streams described herein.

When the content of acetic acid in line 115 is less than 5 wt. %, theacid separation column 107 may be skipped and line 115 may be introduceddirectly to second column 108, also referred to herein as a light endscolumn.

In the embodiment shown in FIG. 1A, line 115 is introduced in the lowerpart of first column 107, e.g., lower half or lower third. In firstcolumn 107, unreacted acetic acid, a portion of the water, and otherheavy components, if present, are removed from the composition in line115 and are withdrawn, preferably continuously, as residue. Some or allof the residue may be returned and/or recycled back to reaction zone 101via line 116. First column 107 also forms an overhead distillate, whichis withdrawn in line 117, and which may be condensed and refluxed, forexample, at a ratio of from 10:1 to 1:10, e.g., from 3:1 to 1:3 or from1:2 to 2:1.

Any of columns 107, 108, or 109 may comprise any distillation columncapable of separation and/or purification. The columns preferablycomprise tray columns having from 1 to 150 trays, e.g., from 10 to 100trays, from 20 to 95 trays or from 30 to 75 trays. The trays may besieve trays, fixed valve trays, movable valve trays, or any othersuitable design known in the art. In other embodiments, a packed columnmay be used. For packed columns, structured packing or random packingmay be employed. The trays or packing may be arranged in one continuouscolumn or they may be arranged in two or more columns such that thevapor from the first section enters the second section while the liquidfrom the second section enters the first section, etc.

The associated condensers and liquid separation vessels that may beemployed with each of the distillation columns may be of anyconventional design and are simplified in FIGS. 1A and 1B. As shown inFIGS. 1A and 1B, heat may be supplied to the base of each column or to acirculating bottom stream through a heat exchanger or reboiler. Othertypes of reboilers, such as internal reboilers, may also be used in someembodiments. The heat that is provided to reboilers may be derived fromany heat generated during the process that is integrated with thereboilers or from an external source such as another heat generatingchemical process or a boiler. Although one reactor and one flasher areshown in FIGS. 1A and 1B, additional reactors, flashers, condensers,heating elements, and other components may be used in embodiments of thepresent invention. As will be recognized by those skilled in the art,various condensers, pumps, compressors, reboilers, drums, valves,connectors, separation vessels, etc., normally employed in carrying outchemical processes may also be combined and employed in the processes ofthe present invention.

The temperatures and pressures employed in any of the columns may vary.As a practical matter, pressures from 10 KPa to 3000 KPa will generallybe employed in these zones although in some embodiments subatmosphericpressures may be employed as well as superatmospheric pressures.Temperatures within the various zones will normally range between theboiling points of the composition removed as the distillate and thecomposition removed as the residue. It will be recognized by thoseskilled in the art that the temperature at a given location in anoperating distillation column is dependant on the composition of thematerial at that location and the pressure of column. In addition, feedrates may vary depending on the size of the production process and, ifdescribed, may be generically referred to in terms of feed weightratios.

When column 107 is operated under standard atmospheric pressure, thetemperature of the residue exiting in line 116 from column 107preferably is from 95° C. to 120° C., e.g., from 105° C. to 117° C. orfrom 110° C. to 115° C. The temperature of the distillate exiting inline 117 from column 107 preferably is from 70° C. to 110° C., e.g.,from 75° C. to 95° C. or from 80° C. to 90° C. In other embodiments, thepressure of first column 107 may range from 0.1 KPa to 510 KPa, e.g.,from 1 KPa to 475 KPa or from 1 KPa to 375 KPa. Exemplary distillate andresidue compositions for first column 107 are provided in Table 3 below.For convenience, the distillate and residue of the first column may alsobe referred to as the “first distillate” or “first residue.” Thedistillates or residues of the other columns may also be referred towith similar numeric modifiers (second, third, etc.) in order todistinguish them from one another, but such modifiers should not beconstrued as requiring any particular separation order.

TABLE 3 FIRST COLUMN Conc. (wt. %) Conc. (wt. %) Conc. (wt. %)Distillate Ethanol 20 to 75 30 to 70 40 to 65 Water 10 to 40 15 to 35 20to 35 Acetic Acid <2 0.001 to 0.5  0.01 to 0.2  Ethyl Acetate <60 5.0 to40  10 to 30 Acetaldehyde <10 0.001 to 5    0.01 to 4   Acetal <0.1 <0.1<0.05 Acetone <0.05 0.001 to 0.03   0.01 to 0.025 Residue Acetic Acid 60 to 100 70 to 95 85 to 92 Water <30  1 to 20  1 to 15 Ethanol <1 <0.9<0.07

As shown in Table 3, without being bound by theory, it has surprisinglyand unexpectedly been discovered that when any amount of acetal isdetected in the feed that is introduced to the acid separation column(first column 107), the acetal appears to decompose in the column suchthat less or even no detectable amounts are present in the distillateand/or residue.

Depending on the reaction conditions, the crude ethanol product exitingreactor 103 in line 112 may comprise ethanol, acetic acid (unconverted),ethyl acetate, and water. After exiting reactor 103, a non-catalyzedequilibrium reaction may occur between the components contained in thecrude ethanol product until it is added to flasher 106 and/or firstcolumn 107. This equilibrium reaction tends to drive the crude ethanolproduct to an equilibrium between ethanol/acetic acid and ethylacetate/water, as shown below.EtOH+HOAc⇄EtOAc+H₂O

In the event the crude ethanol product is temporarily stored, e.g., in aholding tank, prior to being directed to distillation zone 102, extendedresidence times may be encountered. Generally, the longer the residencetime between reaction zone 101 and distillation zone 102, the greaterthe formation of ethyl acetate. For example, when the residence timebetween reaction zone 101 and distillation zone 102 is greater than 5days, significantly more ethyl acetate may form at the expense ofethanol. Thus, shorter residence times between reaction zone 101 anddistillation zone 102 are generally preferred in order to maximize theamount of ethanol formed. In one embodiment, a holding tank (not shown),is included between the reaction zone 101 and distillation zone 102 fortemporarily storing the liquid component from line 115 for up to 5 days,e.g., up to 1 day, or up to 1 hour. In a preferred embodiment no tank isincluded and the condensed liquids are fed directly to the firstdistillation column 107. In addition, the rate at which thenon-catalyzed reaction occurs may increase as the temperature of thecrude ethanol product, e.g., in line 115, increases. These reactionrates may be particularly problematic at temperatures exceeding 30° C.,e.g., exceeding 40° C. or exceeding 50° C. Thus, in one embodiment, thetemperature of liquid components in line 115 or in the optional holdingtank is maintained at a temperature less than 40° C., e.g., less than30° C. or less than 20° C. One or more cooling devices may be used toreduce the temperature of the liquid in line 115.

As discussed above, a holding tank (not shown) may be included betweenthe reaction zone 101 and distillation zone 102 for temporarily storingthe liquid component from line 115, for example from 1 to 24 hours,optionally at a temperature of about 21° C., and corresponding to anethyl acetate formation of from 0.01 wt. % to 1.0 wt. % respectively. Inaddition, the rate at which the non-catalyzed reaction occurs mayincrease as the temperature of the crude ethanol product is increased.For example, as the temperature of the crude ethanol product in line 115increases from 4° C. to 21° C., the rate of ethyl acetate formation mayincrease from about 0.01 wt. % per hour to about 0.005 wt. % per hour.Thus, in one embodiment, the temperature of liquid components in line115 or in the optional holding tank is maintained at a temperature lessthan 21° C., e.g., less than 4° C. or less than −10° C.

In addition, it has now been discovered that the above-describedequilibrium reaction may also favor ethanol formation in the top regionof first column 107.

The distillate, e.g., overhead stream, of column 107 optionally iscondensed and refluxed as shown in FIG. 1A, preferably, at a refluxratio of 1:5 to 10:1. The distillate in line 117 preferably comprisesethanol, ethyl acetate, and water, along with other impurities, whichmay be difficult to separate due to the formation of binary and tertiaryazeotropes. The first distillate also comprises a significantly reducedamount of acetic acid.

The first distillate in line 117 is introduced to the second column 108,also referred to as the “light ends column,” preferably in the middlepart of column 108, e.g., middle half or middle third. As one example,when a 25 tray column is utilized in a column without water extraction,line 117 is introduced at tray 17. Second column 108 may be a traycolumn or packed column. In one embodiment, second column 108 is a traycolumn having from 5 to 70 trays, e.g., from 15 to 50 trays or from 20to 45 trays.

In one embodiment, the second column 108 may be an extractivedistillation column. In such embodiments, an extraction agent, such aswater, may be added to second column 108. If the extraction agentcomprises water, it may be obtained from an external source or from aninternal return/recycle line from one or more of the other columns. In apreferred embodiment, the water in the third residue of third column 109is utilized as the extraction agent.

Although the temperature and pressure of second column 108 may vary,when at atmospheric pressure the temperature of the second residueexiting in line 118 from second column 108 preferably is from 60° C. to90° C., e.g., from 70° C. to 90° C. or from 80° C. to 90° C. Thetemperature of the second distillate exiting in line 120 from secondcolumn 108 preferably is from 50° C. to 90° C., e.g., from 60° C. to 80°C. or from 60° C. to 70° C. Column 108 may operate at atmosphericpressure. In other embodiments, the pressure of second column 108 mayrange from 0.1 KPa to 510 KPa, e.g., from 1 KPa to 475 KPa or from 1 KPato 375 KPa. Exemplary components for the distillate and residuecompositions for second column 108 are provided in Table 4 below. Itshould be understood that the distillate and residue may also containother components, not listed, such as components in the feed.

TABLE 4 SECOND COLUMN Conc. (wt. %) Conc. (wt. %) Conc. (wt. %)Distillate Ethyl Acetate 10 to 90 25 to 90 50 to 90 Acetaldehyde  1 to25  1 to 15 1 to 8 Water  1 to 25  1 to 20  4 to 16 Ethanol <30 0.001 to15   0.01 to 5   Acetal <5 0.001 to 2    0.01 to 1   Residue Water 30 to70 30 to 60 30 to 50 Ethanol 20 to 75 30 to 70 40 to 70 Ethyl Acetate <30.001 to 2    0.001 to 0.5  Acetic Acid <0.5 0.001 to 0.3  0.001 to 0.2 

The weight ratio of ethanol in the second residue to ethanol in thesecond distillate preferably is at least 3:1, e.g., at least 6:1, atleast 8:1, at least 10:1 or at least 15:1. The weight ratio of ethylacetate in the second residue to ethyl acetate in the second distillatepreferably is less than 0.4:1, e.g., less than 0.2:1 or less than 0.1:1.In embodiments that use an extractive column with water as an extractionagent as the second column 108, the weight ratio of ethyl acetate in thesecond residue to ethyl acetate in the second distillate approacheszero.

The second distillate in line 120 preferably is refluxed as shown inFIG. 1A, for example, at a reflux ratio of from 1:10 to 10:1, e.g., from1:5 to 5:1 or from 1:3 to 3:1. The distillate from second column 108 maybe purged. In one embodiment, since the second distillate contains ethylacetate, all or a portion of the distillate from second column 108 maybe recycled to reaction zone 101 via optional line 120′ in order toconvert the ethyl acetate to additional ethanol. As shown in the FIGS.,all or a portion the distillate may be recycled to reactor 103 viaoptional line 120′, and may be co-fed with the acetic acid feed line105. In another embodiments, the second distillate in line 120 may befurther purified to remove impurities, such as acetaldehyde, using oneor more additional columns (not shown).

As shown, the second residue from the bottom of second column 108, whichcomprises ethanol and water, is fed via line 118 to third column 109,also referred to as the “product column.” More preferably, the secondresidue in line 118 is introduced in the lower part of third column 109,e.g., lower half or lower third. Third column 109 recovers ethanol,which preferably is substantially pure other than the azeotropic watercontent, as the distillate in line 119. The distillate of third column109 preferably is refluxed as shown in FIG. 1A, for example, at a refluxratio of from 1:10 to 10:1, e.g., from 1:3 to 3:1 or from 1:2 to 2:1.The third residue in line 121, which preferably comprises primarilywater, preferably is removed from the system 100 or may be partiallyreturned to any portion of the system 100. Third column 109 ispreferably a tray column as described above and preferably operates atatmospheric pressure. The temperature of the third distillate exiting inline 119 from third column 109 preferably is from 60° C. to 110° C.,e.g., from 70° C. to 100° C. or from 75° C. to 95° C. The temperature ofthe third residue exiting from third column 109 preferably is from 70°C. to 115° C., e.g., from 80° C. to 110° C. or from 85° C. to 105° C.,when the column is operated at atmospheric pressure. Exemplarydistillate and residue compositions for third column 109 are provided inTable 5 below. It should be understood that the distillate and residuemay also contain other components, not listed, such as components in thefeed.

TABLE 5 THIRD COLUMN Conc. (wt. %) Conc. (wt. %) Conc. (wt. %)Distillate Ethanol 75 to 96   80 to 96  85 to 96 Water <12  1 to 9  3 to8 Acetic Acid <1 0.001 to 0.1  0.005 to 0.01 Ethyl Acetate <5 0.001 to4   0.01 to 3  Residue Water 75 to 100   80 to 100   90 to 100 Ethanol<0.8 0.001 to 0.5  0.005 to 0.05 Ethyl Acetate <1 0.001 to 0.5 0.005 to0.2 Acetic Acid <2 0.001 to 0.5 0.005 to 0.2

Any of the compounds that are carried through the distillation processfrom the feed or crude reaction product generally remain in the thirddistillate in amounts of less 0.1 wt. %, based on the total weight ofthe third distillate composition, e.g., less than 0.05 wt. % or lessthan 0.02 wt. %. In one embodiment, one or more side streams may removeimpurities from any of the columns 107, 108, and/or 109 in system 100.In one embodiment, at least one side stream may be used to removeimpurities from the third column 109. The impurities may be purgedand/or retained within the system 100.

As discussed above, the third distillate in line 119 preferably isfurther processed to substantially remove water therefrom. The furtherprocessing results in the formation of an anhydrous ethanol productstream, e.g., anhydrous ethanol composition. In one embodiment, thefurther processing employs one or more separation units, e.g.,dehydrators. Examples of suitable dehydrators include an extractivedistillation column 122 (as shown in FIG. 1A); a molecular sieve unit124 (as shown in FIG. 1B); and/or a desiccant (not shown). For example,useful dehydration methods and/or units include those discussed in U.S.Pat. Nos. 4,465,875; 4,559,109; 4,654,123; and 6,375,807. The entiretiesof these patents are hereby incorporated by reference.

Typically, the water and the ethanol in the third distillate form awater/ethanol azeotrope. In one embodiment, the dehydrators of thepresent invention remove the water from the water/ethanol azeotrope inthe third distillate. For example, the dehydration may remove at least50 wt. % of the water from the third distillate, e.g., at least 75 wt.%, at least 90 wt. %, at least 95 wt. %, or at least 99 wt. %. In termsof ranges, the dehydration removes from 50 wt. % to 100 wt. % of thewater from the third distillate, e.g., from 75 wt. % to 99.9999 wt. %,from 90 wt. % to 99.999 wt. %, from 90 wt. % to 99.99 wt. %, from 90 wt.% to 99.9 wt. %, or from 90 wt. % to 99.5 wt. %. The removal of thiswater from the third distillate results in the formation of theanhydrous ethanol composition.

Water-containing stream 128 exiting the dehydrator(s) comprisesprimarily water, e.g., at least 50 wt. % water, e.g., at least 75 wt. %,at least 90 wt. %, at least 95 wt. %, or at least 99 wt. %, andpreferably is removed from system 100. In one embodiment, the fourthresidue 128 may be partially returned to any portion of system 100. In apreferred embodiment, the water may be utilized as an extraction agentin any one of the columns, e.g., second column 108.

In FIG. 1A, the distillate from third column 109, which comprisesethanol/water azeotrope, may be fed, e.g., via line 119, to fourthcolumn 122, also referred to as the “finishing column.” Fourth column122 further separates, e.g., distills, water from the water/ethanolazeotrope in the third distillate. As a result, fourth column 122recovers ethanol that has been further dehydrated as the fourthdistillate in line 126.

Preferably, fourth column 122 is an extractive distillation column thatemploys an extraction agent and preferably operates at atmosphericpressure. Extractive distillation is a vapor-liquid separation process,which uses an additional component to increase the relative volatilityof the components to be separated. In extractive distillation, aselective high boiling solvent is utilized to alter the activitycoefficients and, hence, increase the separation factor of thecomponents. The additional component may be a liquid solvent, an ionicliquid, a dissolved salt, a mixture of volatile liquid solvent anddissolved salt, or hyperbranched polymer.

Fourth column 122 preferably comprises from 1 to 150 trays, e.g., from10 to 100 or from 20 to 70 trays. As indicated above, the trays may besieve trays, fixed valve trays, movable valve trays, or any othersuitable design known in the art. Exemplary extraction agents mayinclude, but are not limited to glycols, glycerol, gasoline, and hexane.The third distillate in line 119 may be introduced to fourth column 122at any level. Preferably, line 119 is introduced into the fourth column122 in the middle part of fourth column 122, e.g., the middle half ormiddle third.

In one embodiment, as shown in FIG. 1B, the distillate from third column109 is fed to a molecular sieve unit 124 comprising molecular sieves. Inthese embodiments, the molecular sieves separate additional water fromthe third distillate in line 119. In some embodiments, molecular sieveunit 124 may be used in place of or in conjunction with the finishingcolumn. Generally speaking, the molecular sieves may be configured in amolecular sieve bed (not shown). In one embodiment, the molecular sievesare selected to remove one or more impurities that may exist in thethird distillate. The selection criteria may include, for example, poresize and volume characteristics. In one embodiment, the molecular sievematerial is selected to remove water, acetic acid, and/or ethyl acetatefrom the third distillate to form the anhydrous ethanol composition.Suitable molecular sieves include, for example, zeolites and molecularsieves 3A, 4A and 5A (commercially available from Aldrich). In anotherembodiment, an inorganic adsorbents such as lithium chloride, silicagel, activated alumina, and/or bio-based adsorbents such as corn grits,may be utilized. In a preferred embodiment, molecular sieve unit 124removes water from the third distillate in the amounts discussed above.

In addition, other separation units, e.g., dehydrating units, such asdesiccant systems and/or membrane systems, may be used, either in placeof or in conjunction with the finishing column and/or the molecularsieve unit discussed above. If multiple dehydrating units are utilized,the dehydrating units, being of the same or of different type, may beutilized in any configuration. Preferably, an extractive distillationcolumn and a membrane system are utilized with one another. Optionally,the molecular sieves are employed in a bed within the finishing column,e.g., at the upper portion thereof.

Other exemplary dehydration processes include azeotropic distillationand membrane separation. In azeotropic distillation, a volatilecomponent, often referred to as an entrainer, is added to the componentsto be separated. The addition of the entrainer forms an azeotrope withthe components, thus changing the relative volatilities thereof. As aresult, the separation factors (activity coefficients) of the componentsare improved. The azeotropic distillation system, in one embodiment,comprises one or more distillation columns, e.g., two or more or threeor more.

Membrane separation, e.g., membrane pervaporation, may also be aneffective and energy-saving process for separating azeotropic mixtures.Generally speaking, pervaporation is based on the solution-diffusionmechanism, which relies on the gradient of the chemical potentialbetween the feed and the permeate sides of the membrane. The membranes,in one embodiment, may be hydrophilic or hydrophobic. Preferably, themembranes are hydrophilic or water permselective due to the smallermolecular size of water. In other embodiments, the membranes arehydrophobic or ethanol permselective. Typically, there are threecategories of membranes that may be used—inorganic, polymeric, andcomposite membrane.

Anhydrous Ethanol Composition

The anhydrous ethanol compositions beneficially comprise ethanol and, ifany, a small amount of water preferably formed via the inventive aceticacid hydrogenation and separation steps. In one embodiment, the term“anhydrous ethanol composition,” as used herein, means a substantiallyanhydrous ethanol composition. For example a substantially anhydrousethanol composition may have a water content of less than 1 wt. % water,e.g., less than 0.5 wt. %, less than 0.1 wt. %, less than 0.01 wt. %,less than 0.001 wt. %, or less than 0.0001 wt. %, based on the totalweight of the substantially anhydrous ethanol composition. Table 6provides exemplary ranges for the water concentration in the anhydrousethanol compositions. Although Table 6 indicated that water ispreferably present in a small amount, in other embodiments, theanhydrous ethanol composition may be completely anhydrous, e.g.,containing no detectable water. In these cases conventional waterdetection methods employed in the industry may be utilized to measurewater content or lack thereof. Preferably, the anhydrous ethanolcomposition comprises at least 95 wt. % ethanol, e.g., at least 95 wt.%, at least 99 wt. %, at least 99.9 wt. %, or at least 99.99 wt. %.Table 6 provides exemplary ranges for the ethanol concentration in theanhydrous ethanol compositions.

In addition to the ethanol and, if any, a small amount of water, theanhydrous ethanol composition may also comprise only trace amounts ofother impurities such as acetic acid; C₃ alcohols, e.g., n-propanol;and/or C₄-C₅ alcohols. Exemplary compositional ranges for the ethanol,the water, and various impurities that may be present in small amounts,if at all, are provided below in Table 6.

TABLE 6 ANHYDROUS ETHANOL COMPOSITIONS Component Conc. (wt. %) Conc.(wt. %) Conc. (wt. %) Ethanol     95 to 100    95 to 99.99    99 to99.90 Water 0.0001 to 1 0.001 to 0.5 0.001 to 0.05 Acetic Acid <1 <0.1<0.01 Ethyl Acetate <2 <0.5 <0.05 Acetal <0.05 <0.01 <0.005 Acetone<0.05 <0.01 <0.005 Isopropanol <0.5 <0.1 <0.05 n-propanol <0.5 <0.1<0.05

The anhydrous ethanol compositions of the present invention preferablycontain very low amounts, e.g., less than 0.5 wt. %, of other alcohols,such as methanol, butanol, isobutanol, isoamyl alcohol and other C₄-C₂₀alcohols.

The anhydrous ethanol compositions of the embodiments of the presentinvention may be suitable for use in a variety of applications includingfuels, solvents, chemical feedstocks, pharmaceutical products,cleansers, sanitizers, or hydrogenation transport. In fuel applications,the anhydrous ethanol composition may be blended with gasoline for motorvehicles such as automobiles, boats and small piston engine aircrafts.In non-fuel applications, the anhydrous ethanol composition may be usedas a solvent for toiletry and cosmetic preparations, detergents,disinfectants, coatings, inks, and pharmaceuticals. The anhydrousethanol composition may also be used as a processing solvent, e.g., inmanufacturing processes for medicinal products, food preparations, dyes,photochemicals and latex processing.

The anhydrous ethanol composition may also be used as a chemicalfeedstock to make other chemicals such as vinegar, ethyl acrylate, ethylacetate, ethylene, glycol ethers, ethylamines, aldehydes, and higheralcohols, especially butanol. The anhydrous ethanol composition may besuitable for use as a feed stock in esters production. Preferably, inthe production of ethyl acetate, the anhydrous ethanol composition maybe esterified with acetic acid or reacted with polyvinyl acetate. Theanhydrous ethanol composition may be dehydrated to produce ethylene. Anyof known dehydration catalysts can be employed to dehydrate ethanol,such as those described in copending U.S. Pub. 20100030001 and20100030002, the entire contents and disclosures of which are herebyincorporated by reference. A zeolite catalyst, for example, may beemployed as the dehydration catalyst. Preferably, the zeolite has a porediameter of at least about 0.6 nm, and preferred zeolites includedehydration catalysts selected from the group consisting of mordenites,ZSM-5, a zeolite X and a zeolite Y. Zeolite X is described, for example,in U.S. Pat. No. 2,882,244 and zeolite Y in U.S. Pat. No. 3,130,007, theentireties of which are hereby incorporated by reference.

EXAMPLES Example 1

Crude ethanol product samples were prepared via acetic acidhydrogenation as discussed above. The samples comprised ethanol, aceticacid, acetaldehyde, water, and ethyl acetate.

Each of the crude ethanol product samples was purified using first,second, and third columns as shown in FIG. 1A. In each case, the thirddistillate, yielded from the respective crude ethanol product sample,was analyzed. The average compositional values of the third distillateare provided in Table 7.

TABLE 7 Third Distillate Component (avg. wt. %) Ethanol 92.27 Water 7.7Ethyl Acetate 0.008 Acetaldehyde 0.0002 Acetic Acid 0.0001 Isopropanol0.0118 N-propanol 0.0127 Acetone 0 Acetal 0.0001

The third distillates, when dehydrated as discussed above, provide foranhydrous ethanol compositions having the average compositional valuesare provided in Table 8. As shown in Table 8, the anhydrous ethanolcompositions that may be formed via the inventive acetic acidhydrogenation and separation steps, comprise ethanol and, if any, asmall amount of water.

TABLE 8 Anhydrous Ethanol Compositions Component (avg. wt. %) Ethanol99.46 Water 0.50 Ethyl Acetate 0.009 Acetaldehyde 0.0002 Acetic Acid0.0001 Isopropanol 0.0127 N-propanol 0.0131 Acetone 0 Acetal 0.0001

While the invention has been described in detail, modifications withinthe spirit and scope of the invention will be readily apparent to thoseof skill in the art. In view of the foregoing discussion, relevantknowledge in the art and references discussed above in connection withthe Background and Detailed Description, the disclosures of which areall incorporated herein by reference. In addition, it should beunderstood that aspects of the invention and portions of variousembodiments and various features recited below and/or in the appendedclaims may be combined or interchanged either in whole or in part. Inthe foregoing descriptions of the various embodiments, those embodimentswhich refer to another embodiment may be appropriately combined withother embodiments as will be appreciated by one of skill in the art.Furthermore, those of ordinary skill in the art will appreciate that theforegoing description is by way of example only, and is not intended tolimit the invention.

We claim:
 1. A process for producing an anhydrous ethanol composition,the process comprising: hydrogenating acetic acid in the presence of acatalyst to form a crude ethanol product; separating in a first columnat least a portion of the crude ethanol product into a first distillatecomprising ethanol, water and ethyl acetate, and a first residuecomprising acetic acid; separating in a second column at least a portionof the first distillate into a second distillate comprising ethylacetate and a second residue comprising ethanol and water; separating ina third column at least a portion of the second residue into a thirddistillate comprising ethanol and residual water and a third residuecomprising separated water; and dehydrating at least a portion of thethird distillate to form the anhydrous ethanol composition comprisingless than 1 wt. % water, based on the total weight of the anhydrousethanol composition.
 2. The process of claim 1, wherein the anhydrousethanol composition, comprises less than 0.1 wt. % water.
 3. The processof claim 1, wherein the anhydrous ethanol composition, comprises from 95wt. % to 99.9999 wt. % ethanol; and from 0.0001 wt. % to 1 wt. % water.4. The process of claim 1, wherein the third distillate comprises from0.0001 wt. % to 12 wt. % water.
 5. The process of claim 1, wherein thedehydrating removes at least 50 wt. % of the water from the thirddistillate.
 6. The process of claim 1, wherein the dehydrating comprisesseparating, in a fourth column, at least a portion of the thirddistillate into a fourth distillate comprising the anhydrous ethanolcomposition and a fourth residue comprising water.
 7. The process ofclaim 6, wherein the anhydrous ethanol composition comprises from 0.001wt. % to 0.5 wt. % water.
 8. The process of claim 6, wherein thedehydrating is performed via an extractive distillation column thatemploys at least one extraction agent selected from the group consistingof glycols, glycerol, gasoline, and hexane.
 9. The process of claim 1,wherein the dehydrating is performed via a molecular sieve unitcomprising molecular sieves.
 10. A process for producing an anhydrousethanol composition, the process comprising: hydrogenating acetic acidin the presence of a catalyst to form a crude ethanol product;separating at least a portion of the crude ethanol product in one ormore separation units to form the anhydrous ethanol compositioncomprising less than 1 wt. % water, based on the total weight of theanhydrous ethanol composition.